The present invention relates to cementing operations and, more particularly, in certain embodiments, to cement compositions comprising particulate foamed elastomers and associated methods.
Cement compositions may be used in a variety of subterranean applications. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like.
Set cement in wells, and particularly the set cement sheath in the annulus of a well, may fail due to, inter alia, shear, tensile and compressional stresses exerted on the set cement. There are several stressful conditions that have been associated with well bore cement failures. One example of such a condition results from the relatively high fluid pressures and/or temperatures inside of the set casing during testing, perforation, fluid injection, or fluid production. If the pressure and/or temperature inside the pipe increases, the resultant internal pressure may expand the pipe, both radially and longitudinally. This expansion generally may place stress on the cement surrounding the casing causing it to crack, or the bond between the outside surface of the pipe and the cement sheath to fail in the form of, inter alia, loss of hydraulic seal. Another example of such a stressful condition is where the fluids trapped in a cement sheath thermally expand potentially causing high pressures within the sheath itself. This condition often occurs as a result of high temperature differentials created during production or injection of high temperature fluids through the well bore, e.g., wells subjected to steam recovery processes or the production of hot formation fluids. Other stressful conditions that can lead to cement failures include the forces exerted by shifts in the subterranean formations surrounding the well bore or other over-burdened pressures.
Failure of cement within the well bore can result in cracking of the cement as well as a breakdown of the bonds between the cement and the pipe or between the cement sheath and the surrounding subterranean formations. Such failures can result in at least lost production, environmental pollution, hazardous rig operations, and/or hazardous production operations. A common result is the undesirable presence of pressure at the well head in the form of trapped gas between casing strings. Additionally, cement failures can be particularly problematic in multi-lateral wells, which include vertical or deviated (including horizontal) principal well bores having one or more ancillary, laterally extending well bores connected thereto.
Elastomeric materials, such as rubber particles, have previously been included in cement compositions to modify the mechanical properties of the set cement, including Young's Modulus, Poisson's Ration, and the compressive and tensile strength. However, these elastomeric materials may segregate during the placing and setting of the cement, leading to an undesirable density gradient in the set cement.